Acoustic guidance system

ABSTRACT

An acoustic homing system for an antisubmarine weapon having an explosive charge (rocket depth charge, torpedo and the like) which steers the weapon closer to a submerged target after detection while said weapon is sinking in the water. An acoustic transducer detects the target and derives steering signals for movable fins or rudder elements to change the course of the weapon.

United States Patent Mentcher et al.

[ 1 Mar. 14, 1972 [54] ACOUSTIC GUIDANCE SYSTEM [72] Inventors: Israel Mentcher, Trenton, N.J.; Charles E.

Thomas, Scotia, NY.

[73] Assignee: General Electric Company [22] Filed: Dec. 26, 1967 21 Appl. No.: 695,310

521 u.s.c1. Q. ..114/23,102/7 [51 mm ..F42b19/06,F42b l9/0l,F42bl7/00 5s] FieldofSearch ..114/23 [56] References Cited UNITED STATES PATENTS 2,719,486 10/1955 Plumley etal. ....102/70.2 2,965,028 l2/l960 Woodward,-Jr.etal... ..102/7 3,004,508 10/1961 Dickieson ..114/23 3,024,755 3/1962 Brooks ..1 14/23 3,031,644 4/1962 l-lisserich et al. .l02/70.2 3,089,451 5/1963 Gardiner ..1 14/23 3,145,679 8/1964 Brooks ..1 14/23 Primary Examiner-Benjamin A. Borchelt Assistant ExaminerThomas H. Webb Attorney-Francis K. Richwine, Joseph B. Forman, Carl W. Baker, Frank L. Neuhauser and Oscar B. Waddell [57] ABSTRACT An acoustic homing system for an antisubmarine weapon having an explosive charge (rocket depth charge, torpedo and the like) which steers the weapon closer to a submerged target after detection while said weapon is sinking in the water. An acoustic transducer detects the target and derives steering signals for movable fins or rudder elements to change the course of the weapon.

9 Claims, 5 Drawing Figures Patented Mhrchll, 1972 3,648,636

4 Sheets-Sheet 1 INVENTORS ISRAEL MENTCHER CHARLES E.THOMAS THEIR ATT ORNE Y Patented March 14, 1972 3,648,636-

4 sheets-sheet 3 AMPLIFIER l3 g 29 3| SPLIT-L085 I 2 STERING DIRECTION c:

REL TRANSMITTE TRANSDUCER A R a CONTROL AMPLIFIER ss FIG. 2

' l 39 r ARMIMG POWER CIRCUIT SUPPLY PROXIMITY CONTACT 2. TRANSDUCER FUSE 47 49 TIME LIM'T DETONATOR v FIG. 3

INVENTORS ISRAEL MENTCHER HARLES E.THOMAS THEIR ATTORNEY Patented March 14, 1972 3,648,636

' 4 Sheets-Sheet 5 F] G 4 INVENTORS ISRAEL MEN TCHER CHARLES E.THOMAS THEIR ATTORNEY Patented March 14, 1972 4 Sheets-Sheet 4 mm 5 mm mvw MG @8205 :2: m2 $3355 E2285 mm y v J m mid? 552925 J I w U 3 32,3 m w w 23% $3335 .6528 5:850 O 3 -C Em @zEmEw a .m mm @N amid? INVENTORS ISRAEL MENTCHER CHARLES E. THOMAS FIG; 5

THEIR A T TORNEY ACOUSTIC GUIDANCE SYSTEM DESCRIPTION OF THE INVENTION This invention pertains to a target acquisition system for an antisubmarine weapon having an explosive charge which provides guidance to the target after entry of the weapon into the water. More particularly, this invention pertains to an acoustic guidance system for antisubmarine weapons generally having means adapted to steer the weaponcloser to an underwater target while said weapon sinks in the water. Specifically, this invention provides an acoustic guidance system for antisubmarine weapons having negative buoyancy which steers the weapon closer to the target as it sinks in the water.

One class of weapons designed to destroy submerged targets includes bombs, depth charges and antisubmarine rockets whose underwater propulsive force is derived from the negative buoyancy of the device. The underwater trajectory of such a device is essentially vertical after a short period when it is influenced significantly by the angle and velocity of water entry. If the device is to succeed in its mission in destroying its target, such as a submarine, this essentially vertical trajectory must bring the device either into direct contact with the target or within the range from the target less than effective range of the warhead with which the device is equipped. Since most devices cannot carry enough explosive to destroy a target at ranges beyond a few yards, the effective range is severely limited requiring that large numbers of the device by dropped in a systematic pattern or salvo-firing means be adopted in order to achieve any likely probability of destroying the target. For a successful practice the weapon system has included elaborate shipboard fire conu'ol instrumentation in order to lay the weapon into the water as close as possible to the geographical coordinates of the submerged target. While improvements have been made in sonar instrumentation for measuring the position of submarines and the like as well as in the fire control instrumentation, there still remains the basic problem of directing the weapon to the target after the weapon has entered the water. Operational undersea weapons which sink in the water are still fired by means preset before release which include a pressure switch or proximity fuse. In all cases the released weapon is unable to pursue submerged targets which alter course.

By contrast, modern torpedoes are equipped with acoustic guidance systems which enable the weapon to pursue a moving target although evasive action is taken. The guidance system directs the weapon in a programmed search pattern until the target has been detected whereupon an attack mode of operation is initiated. A single acoustic system which combines the acquisition and attack capabilities is ordinarily employed. The acoustic system employs transducers to sense the range and/or bearing of the submerged target and is battery powered to provide control signals to the steering mechanism of the weapon. The torpedo is propelled in the water during the acquisition as well as the attack modes. Constant propulsion of the torpedo after release from the launcher has a number of disadvantages, however, including detection by the target from noise of the propulsion means, rapid use of the propulsion power supply and a relatively long period of time expenditure in searching a given underwater area. Since torpedoes have negative buoyancy this class of antisubmarine weapons can also be enabled to practice the present invention and thereby overcome the foregoing mentioned disadvantages.

This invention provides an acoustic guidance system for antisubmarine weapons generally that improves target acquisition.

Yet another important object of the invention is to provide a target acquisition system for a naval torpedo having propulsion means to pursue a submerged target which includes an acoustic guidance subsystem to steer the torpedo closer to said target while the torpedo sinks in the water. In its broadest sense, the present invention provides means for an antisubmarine weapon to acquire a submerged target by causing the weapon to descend in a substantially vertical direction, actuating acoustic transducer means to detect the presence of the target, and controlling steering means of the weapon by the acoustic transducer signal to direct the course of the weapon closer to the target after acquisition. The antisubmarine weapon is guided toward the target by steering rudders, fins and the like being controlled by electrical signals generated from the acoustic transducer means. If said weapon also has propulsion means, the propulsion power is not turned on during the sink search which serves to minimize interference with the acoustic portion of the system especially where a passive transducer is used. Once the target has been detected, an antisubmarine weapon having propulsion means can actuate said means to commence an attack mode under power and prevent a moving target from escape. An active transducer is preferred as the detection sensor for the antisubmarine weapon to increase the probability of target acquisition during vertical descent, particularly if the target is silent.

Other objects, features and advantages of the present invention will be appreciated more readily by reference to the following detailed description when considered in connection with the accompanying drawings in which:

FIG. 1 is an outline drawing which depicts a preferred embodiment of the invention,

FIG. 2 is a functional block diagram of an acoustic guidance system which can be used in the FIG. 1 embodiment,

FIG. 3 is a block diagram showing a proximity fuse mechanism which can be utilized in practice of the invention,

FIG. 4 is an outline drawing of a different embodiment for the antisubmarine weapon of the invention, and

FIG. 5 is a functional block diagram of a composite acoustic guidance system for practice of the invention.

In FIG. 1 an antisubmarine rocket l is shown seeking a submerged submarine 3 in the ocean 5. The rocket includes an acoustic guidance system 7 which has for essential components a sonic transducer element 9, a transmitter 11 connected to supply an acoustic signal to the transducer, and a receiver 13 which generates a control signal used to steer the rocket under water from the echo signals received by the transducer. The transmitter signal can be sine wave or noise, pulsed or continuous wave, constant frequency or frequency modulated, and electrical circuits for such purposes are all conventional, thereby dispensing with any need for a detailed description herein. Transducer element 9 is of a multilobe construction and is positioned centrally at the nose end of the rocket to provide a plurality of acoustic beams l5, l7, and 19. The operative characteristics of the transducer and transmitter combination are selected to provide an overlapping composite acoustic beam pattern having equal coverage in all directions radially outward from the longitudinal axis 21 of the rocket and project such a composite beam for a distance many times the rocket length. The FIG. 1 drawing is not to scale and the effective range of the acoustic beam will be based upon the particular needs of a given application. For simplicity of construction, the same transducer 9 which projects the acoustic beam is also adapted to receive target echoes although it is entirely possible that in certain applications it will prove advantageous to receive the echoes with a separate transducer. Output signals generated in the transducer from thetarget echoes are compared individually or in groups in order to determine the approximate direction of the target. The basis for signal comparison can be signal amplitude, phase, or degree of statistical correlation, with such comparison taking place in the receiver 13 of the acoustic guidance system. Receivers are available which can process the echo signals in the manner indicated and the FIG. 2 block diagram to be described in detail hereafter discloses one suitable type of receiver. The processes signals from the receiver are applied to control circuits for rudder elements 23. Detonation means 25 includes a conventional firing circuit (not shown) which is supplied with the electrical signals applied to the transducer as well as the output signals therefrom and measures the time interval therebetween for generation of a tiring signal when the weapon is within effective range of the target. The time interval may be measured directly or it may be obtained indirectly as by measuring the frequency of the returning echo signal from a frequency modulated transmisrion.

in operation the rocket enters the water at some trajectory fixed by the launcher and after a few projectile lengths in the water begins a substantially vertical descent toward the ocean bottom. The acoustic guidance system projects a composite beam along the longitudinal axis of the rocket in the water which precedes the underwater rocket path. Detection of a rsubmerged target 3 within the insonified volume produces an echo signal which is received by the transducer 9 and used to generate steering information for the rocket. The echoes received by the individual lobes of said transducer are converted to electrical signals for comparison in order to generate a control signal used to steer the rocket closer to the target. In the particular type of receiver hereinafter described in greater detail, differences in the amplitude and phase of the converted echo signals control steering rudders 23 affixed to the rocket which can alter its vertical descent to some new path at an angle thereto. 1n the FIG. 2 embodiment guidance system a dual channel receiver is used which processes the echo signals reflected from the target into each transducer lobe separately rn order to effect a comparison of the amplitude and phase characteristics for supply to the steering control circuits. Amplitude of the combined signals provides a steering signal in one direction whereas phase difference between said signals furnishes the steering signal in a different direction. The rudders are moved responsive to said signals for turning the weapon in the target direction.

A collision course type of steering is needed for targets moving faster than the sink rate of the rocket. For collision course steering the acoustic guidance system determines range. bearing and speed of the target and thereupon sets a course which will intercept the faster moving target. Repeat echoes from the acoustic guidance system permit further change of course by the rocket in the event of evasive action being taken by the target. The path of the rocket on a collision steering course with a target consists of a relatively straight lline between the point of entry into the water of the rocket and the intercept point if the target continues its original bearrng and speed. Variation in target movement produces need for path changes to a new intercept point. On the other hand, it will be possible to adopt a pursuit type of steering for the rocket when the target moves at a speed much slower than rink rate of descent. Both types of steering can be performed with the acoustic guidance system disclosed in FIG. 2.

A suitable acoustic guidance system for use in practice of the invention is shown in FIG. 2. Basically, said system includes a split lobe direction transducer element 9 in combination with a transmitter ll and a receiver 13. The system further includes comparator 27 and the steering control circuitry 29 which provide control signals for conventional drive means (not shown) operating rudders or tins of the weapon. Transmitter 11 provides an electrical pulse through relay 31 to each lobe of the direction transducer for conversion into acoustic signals and transmission into the water. Echoes reflected from the target are transmitted back to each lobe of raid transducer for conversion into electrical signals and processing in separate channels of the receiver. Amplifiers 33 and 35 are conventional in character and include known circuitry to convert phase difference between signals generated in each half of the transducer into amplitude difi'erences and conventional time variable gain circuitry which makes the receiver insensitive to reverberation echo signals. Amplitude difference between the signals in each channel is measured in the comparator bridge circuit which is also adapted to generate a control signal from the phase difference of said signals for passage to the steering control circuitry 29.

in operation, the above-described acoustic system for the antisubmarine weapon locates a submerged target and steers the weapon toward said target. Range of the target from the weapon is established from duration of the signal travel time to provide an actuation signal for the detonation means of the weapon when it is within lethal range. Selection of an acoustic proximity fuse mechanism for the detonation means permits the weapon to be fired when the echo range signals stop decreasing. For a moving target acquisition, the transducer element in the acoustic guidance system will advantageously be of the wide beam type for reception of echo signals in spite of relative motion between the weapon and target. Likewise, the transducer element of the acoustic proximity fuse mechanism should have an acoustic beam with sufficient coverage to insonify the target in a near-miss situation. Activation of the acoustic guidance system can be delayed until the weapon has progressed to some predetermined depth in the water to avoid any acoustic disturbance caused by water entry and preclude a further possibility of premature detonation during handling and release of the weapon.

FIG. 3 represents a suitable acoustic proximity fuse mechanism for use in combination with the acoustic guidance system of the antisubmarine weapon. Advantageously, said mechanism also contains the contact fuse to detonate the main explosive charge of the weapon upon impact with the submerged target in the event of proximity fuse malfunction. Self-contained proximity fuse devices are known which include both the contact fuse and a transducer element serving as the proximity sensor along with a battery power supply. Said proximity fuse mechanism can be located in the central body of the antisubmarine weapon behind the nose section for detonation when the weapon passes by the target. A striker for the contact fuse operated by inertia forces obviates any need to have the fuse itself strike the target. As will be noted from the detailed description of the FIG. 3 embodiment which follows, the proximity fuse mechanism is entirely separate and distinct from the acoustic guidance system for the antisubmarine weapon. The signal handling elements of said mechanism can be simplified compared to like components in the acoustic guidance system by reason of lesser requirements with respect to range and varying of the target. The signal handling elements of said mechanism need only indicate when the weapon is within a predetermined range from the target in order to detonate the explosive charge. An electrical circuit measuring the time interval between transmitted pulses and reflected echo signals from the proximity transducer element provides this function. The proximity transducer can be selected to have a relatively narrow acoustic beam for more accurate target resolution with respect to the weapon when it is located for signal transmission outwardly from the side of the weapon. it is within contemplation of the invention, however. to employ a single acoustic guidance system having capability to first perform the target acquisition function and thereafter perform the proximity fuse function as both above described by selection of multipurpose components for the particular application.

Accordingly, the FIG. 3 proximity fuse mechanism embodiment contains a power supply 39 of electrical energy for an arming circuit 41 which enables the contact fuse 43 to operate and actuates an active proximity transducer element 45 along an included transmitter circuit. Time limit circuit 47 is connected to receive pulses generated in said transducer together with returned echo signals by known techniques for underwater echo-ranging systems. Proximity to the target is established from duration of signal travel time in said time limit circuit to generate a firing signal for actuation of detonator 49. Said detonator contains the initiating chain for ignition of the main explosive charge in the weapon.

in operation, the firing signal is advantageously delayed by circuit means until the weapon is at the closest distance from the target within the lethal range. At this distance the duration of signal travel time stops decreasing and a further delay can be introduced into the time limit circuit for reception of one or more longer time duration signals generated as the weapon passes by the target to reduce the probability of false triggering. The time interval may be measured directly in known fashion or it may be obtained indirectly, as by measuring the frequency of the echo returning from a frequency modulated transmission. if the proximity transducer element has separate echo lobes, the firing signal can be generated upon receipt of an echo within the lethal range in the lagging lobe with respect to the target. Operation of said transducer at relatively high signal frequency and short pulse duration optimizes determination of the closest distance within the lethal range. Additionally, selection of a detection threshold for said transducer which is high enough so that only echoes from large targets can be detected near the end of the listening period will help avoid false triggering of the weapon.

FIG. 4 represents a schematic external view of an antisubmarine weapon having an acoustic guidance system located at the nose section which cooperates with a separate acoustic proximity fuse mechanism located in the central body section to provide the near-miss correction system of the invention. Said proximity fuse mechanism includes a transducer element positioned on the exterior side wall of the weapon which is adapted to transmit and receive a narrow acoustic beam in a lateral direction with respect to the longitudinal axis of the weapon. In the description for said embodiment which follows, identical numerals are used for the same components of the weapon previously identified to facilitate understanding. Accordingly, antisubmarine weapon 51 has an acoustic guidance system made up of a split lobe direction transducer 9 which cooperates with transmitter 11 and receiver 13, all located in the nose section of the device. The receiver provides control signals for movable fins or rudder elements 23 to direct the weapon closer to a submerged target after entry into the water. Proximity fuse mechanism 37 is disposed rearwardly of said acoustic guidance system in the central body section of the weapon and includes a narrow beam transducer element 45 for detection of the target within the lethal range. A firing signal for the detonator 49 is generated in the proximity fuse mechanism when the weapon has been guided to the closest distance from the target which can be achieved with the acoustic guidance system. The power supply for said proximity fuse mechanism can be actuated by conventional range switch means when the weapon first enters the lethal range.

ln FlG. 5 there is shown a functional block diagram for a combined acoustic guidance system and proximity fuse mechanism which can be utilized in the practice of the invention. Again, the same numerals are used to designate components of the weapon previously identified for greater clarity of understanding. The particular embodiment uses some common signal processing circuitry for acoustic signals developed in the direction transducer and proximity transducer elements of the weapon. As previously mentioned, it is within contemplation of the invention to employ a single transducer element of conventional multilobe construction to generate all acoustic signals needed for initial target detection, steering the weapon closer to the target, and generating the firing signal for the detonator means. Transmitter 11 in the FIG. 5 embodiment furnishes pulse signals through relay 31 to the split lobe direction transducer element 9. Echo signals received from the detected target in said transducer element are supplied to amplifiers 33 and 35 which cooperate with comparator 27 to provide the steering control signals. The output signals from said comparator are supplied to conventional drive means for the movable rudder components of the steering control 29. A range switch 53 includes relay means to enable signal processing in the transmitter and receiver portions of the acoustic guidance system for proximity transducer element 45 at some predetermined distance adjacent to or within the further limit of the lethal range. Additional relay means 55 are provided between the range switch and proximity transducer to operate the latter element sequentially in the transmit and listening modes. Accordingly, transmitter pulses are supplied to said proximity transducer which is connected to a time limit circuit 47 to provide duration of signal travel time in order to generate the firing signal. The firing signal is applied to detonator 49 for ignition of the main explosive charge in the weapon.

As will be evident from the foregoing description, a target acquisition system for an antisubmarine weapon has been provided which steers the weapon closer to the target as it sinks in the water. It is not intended to limit the invention to the specific embodiments above disclosed, however, since it will be evident that changes and modifications can be made thereto without departing from this invention. For example, it is contemplated that antisubmarine weapons having propulsion means can be modified to include the essential features of the above-disclosed system for cooperation to initiate a pursuit attack upon the target after acquisition during the sink search. it is intended to limit the present invention, therefore, only to the scope of the following claims:

What is claimed as new and desired to be secured by Letters Patent in the United States is:

l. A target acquisition system for an antisubmarine weapon having an explosive charge which includes negative buoyancy means to cause the antisubmarine weapon to descend in the water in a substantially vertical direction, acoustic transducer means to detect the presence of an underwater target as the antisubmarine weapon is sinking in the water, steering means responsive to said transducer means to direct the course of said weapon closer to the target while said weapon is sinking in the water, and detonator means to explode the charge when said weapon is within the lethal range of the target.

2. A target acquisition system as in claim 1 wherein the transducer means comprises a multilobe acoustic transducer for transmitting and receiving sound signals.

3. A target acquisition system as in claim 1 wherein the detonator means is actuated by a separate acoustic transducer which derives a firing signal based upon signal travel time for the acoustic signals generated in said transducer.

4. A target acquisition system as in claim 3 wherein said detonator means also includes means to delay the firing signal until there has been repeated indication that the weapon is within lethal range of the target.

5. A target acquisition system as in claim 3 wherein said detonator means includes the combination of a contact fuse and a proximity fuse.

6. A target acquisition system for an antisubmarine weapon having an explosive charge which includes acoustic transducer means to detect the presence of an underwater target as said weapon sinks in the water said acoustic transducer means comprising a multilobe transducer for transmitting and receiving sound signals, electronic circuit means for comparing. signals received by the individual lobes of said acoustic transducer means to generate target direction information, steering means controlled by the signals generated in said electronic circuit means to direct the course of said weapon closer to the target while the weapon is sinking in the water, and detonator means to explode the charge when the time interval between the acoustic signals being transmitted and received provides the indication that the weapon is within a predetermined range from the target.

7. A target acquisition system as in claim 6 wherein the detonator means includes a separate transducer element which cooperates with electronic circuit means to derive a firing signal based upon signal travel time for the acoustic signal generated in said transducer.

8. A target acquisition system as in claim 6 wherein the acoustic transducer means to detect the presence of an underwater target is located in the nose section of the weapon and the detonator means is located in the central body portion of the weapon such that its transducer element projects a lateral beam with respect to the longitudinal axis of the weapon.

9. A target acquisition system as in claim 8 wherein the acoustic transducer means to detect the presence of an underwater target includes a transmitter and receiver which processes the acoustic signals for both transducer elements. 

1. A target acquisition system for an antisubmarine weapon having an explosive charge which includes negative buoyancy means to cause the antisubmarine weapon to descend in the water in a substantially vertical direction, acoustic transducer means to detect the presence of an underwater target as the antisubmarine weapon is sinking in the water, steering means responsive to said transducer means to direct the course of said weapon closer to the target while said weApon is sinking in the water, and detonator means to explode the charge when said weapon is within the lethal range of the target.
 2. A target acquisition system as in claim 1 wherein the transducer means comprises a multilobe acoustic transducer for transmitting and receiving sound signals.
 3. A target acquisition system as in claim 1 wherein the detonator means is actuated by a separate acoustic transducer which derives a firing signal based upon signal travel time for the acoustic signals generated in said transducer.
 4. A target acquisition system as in claim 3 wherein said detonator means also includes means to delay the firing signal until there has been repeated indication that the weapon is within lethal range of the target.
 5. A target acquisition system as in claim 3 wherein said detonator means includes the combination of a contact fuse and a proximity fuse.
 6. A target acquisition system for an antisubmarine weapon having an explosive charge which includes acoustic transducer means to detect the presence of an underwater target as said weapon sinks in the water, said acoustic transducer means comprising a multilobe transducer for transmitting and receiving sound signals, electronic circuit means for comparing signals received by the individual lobes of said acoustic transducer means to generate target direction information, steering means controlled by the signals generated in said electronic circuit means to direct the course of said weapon closer to the target while the weapon is sinking in the water, and detonator means to explode the charge when the time interval between the acoustic signals being transmitted and received provides the indication that the weapon is within a predetermined range from the target.
 7. A target acquisition system as in claim 6 wherein the detonator means includes a separate transducer element which cooperates with electronic circuit means to derive a firing signal based upon signal travel time for the acoustic signal generated in said transducer.
 8. A target acquisition system as in claim 6 wherein the acoustic transducer means to detect the presence of an underwater target is located in the nose section of the weapon and the detonator means is located in the central body portion of the weapon such that its transducer element projects a lateral beam with respect to the longitudinal axis of the weapon.
 9. A target acquisition system as in claim 8 wherein the acoustic transducer means to detect the presence of an underwater target includes a transmitter and receiver which processes the acoustic signals for both transducer elements. 